Is there an easy way to find a user by email address?

You can follow those steps:

First check for roles access in Users and Permission plugin

Then Goto Settings → USERS & PERMISSIONS PLUGIN → Roles,

You will get Roles page, if you haven’t created any roles you will see default two roles,as below
Authenticated
Public

Click on public → goto Users-Permissions.

In Users-Permissions Goto USER section → Tick mark “find” checkbox and save it
and hit this Api-Endpoint with filtering.

GET /api/users?filters[$and][0][email][$eq]=some@email.com

Note: If you want query all your api end-points from authenticated Role you need provide jwt Token in your request.